Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $151.52   4.322%   $158.0687   $158.07   $158.05   $158.10  
  Purchase #2 $153.77   6.178%   $163.2699   $163.27   $163.25   $163.30  
  Purchase #3 $29.82   6.619%   $31.7938   $31.79   $31.80   $31.80  
  Purchase #4 $134.76   3.702%   $139.7488   $139.75   $139.75   $139.70  
  Purchase #5 $29.94   3.651%   $31.0331   $31.03   $31.05   $31.00  
  Purchase #6 $70.66   3.637%   $73.2299   $73.23   $73.25   $73.20  
  Purchase #7 $84.29   10.125%   $92.8244   $92.82   $92.80   $92.80  
  7 purchase totals = $654.76       $689.9686   $689.96   $689.95   $689.90